Pulse driver with magnetic amplitude and width control



Jan. 8, 1963 E. F. MYERs ETAL 3,072,802

PULSE DRIVER WITH MAGNETIC AMPLITUDE AND WIDTH CONTROL Filed Jan. 14,1959 l4 Ib NNC '3 LOAD DEGENERATIVE Q FEEDBACK 25 REGENERATIVE g9FEEDBACK 2 SUCCEEDING DRIVER STAGE INVENTORS EDWARD F. MYERS BY EDwARDw. YOUNG United States Patent PULSE DRIVER wrTIr MAGNETIC AMPLITUDE ANDWIDTH CONTROL Edward F. Myers, Yeadon, and Edward William Young,Philadelphia, Pa., assignors to Burroughs Corporation, Detroit, Mich., acorporation of Michigan Filed Jan. 14, 1959, Ser. No. 786,789 5 Claims.(Cl. 30788.5)

This invention relates to pulse-forming circuits and more particularlyto a novel driving circuit for providing current pulses havingcontrolled amplitudes and widths.

A variety of circuits for supplying constant current pulses to a loadare well-known in the electronics art. In order to achieve the desiredcurrent regulation, present day current drivers employ complicatedcircuits which waste space, are inefficient, and ultimately lessen theoverall dependability of the system in which they are used.

The present invention is characterized by inherent current regulationachieved with economy of components and simplicity of design. Theregulation results from the action of two pulse transformers on acurrent amplifying device. The degree of conduction of the currentdevice, subsequent to the application of a trigger pulse thereto, is theresultant of the respective regenerative and degenerative effects of thepulse transformers on the current device. One of the transformers isadapted to shape the current pulse while the other controls itsamplitude. If desired, a number of driver circuits may be operated intandem by allowing the current pulse of one driver to trigger thesucceeding driver. This latter technique is particularly useful inoperating different elements of magnetic shift registers for matrixstorage systems which require a plurality of sequential interrogationpulses. Thus, by combining two or more of the instant driver circuits, agenerator is obtained which may be triggered to deliver a sequence oftwo or more timed current waveforms.

Although not limited thereto, a preferred embodiment of the instantinvention utilizes one transistor as the drive means and a pair of pulsetransformers as control means; thereby combining the inherent advantagesof the solid state components with those of the circuit configuration.

Accordingly, it is a general object of the invention to provide animproved pulse-forming circuit for generating current pulses.

Another object of the invention is to provide driving circuits fordelivering a sequence of current pulse waveforms.

A further object of the invention is to provide a current driver circuithaving the combined advantages of simplicity, efficiency and economy.

A still further object of the invention is to provide a driver circuitwhich utilizes exclusively solid state electronic components.

A more specific object of the present invention is to provide aself-regulating pulse-forming circuit which makes use of the respectiveregenerative and degenerative effects of a pair of pulse transformers onthe conduction of an amplifier device.

These and other features of the invention are apparent from thepreferred embodiment described in the following, with reference to thedrawing which is a schematic diagram of the current driver according tothe instant invention.

Referring now to the drawing, there is shown an illus trative embodimentof the present invention comprising a PNP transistor having an emitter11, base 12, and a collector electrode 13, a first pulse transformer 20having a primary winding 21 and two secondary windings 3,072,802Patented Jan. 8, 1963 2 22 and 23 respectively, and a second pulsetransformer 30 having a primary winding 31 and a secondary winding 32.It should be noted that the invention is not restricted to the use of aPNP-type transistor, but may employ other types in accordance withestablished design procedures well known to those skilled in the art.

With respect to the transformers, the polarities of the voltagesdeveloped across the same windings coupled thereto are material to theoperation of the circuit. Therefore a dot has been aflixed adjacent thatend of each Winding which has the same polarity of voltages with respectto the other end thereof, as every other winding so designated, for apredetermined direction of magnetization of the transformer core.

A. trigger pulse source 50 is connected to input terminal 15. Blockingdiode 14 allows only trigger pulses of the proper polarity to pass tothe base electrode 12 of transistor 10. Emitter electrode 11 isconnected to ground potential. Collector electrode 13 is connected to asource of negative potential E by means of a circuit comprising the load40, primary winding 31 of transformer 30, and primary winding 21 oftransformer 20. A diode 24 is connected in parallel with transformerwinding 21. The base electrode 12 of transistor 10 is returned to groundpotential through a circuit comprising the parallel combination ofsecondary winding 32 and resistor 33, and secondary winding 22. Aclamping diode 25 is connected between the dotted terminal of winding 22and the collector supply voltage E An additional secondary winding 23 iscoupled to transformer 20. A capacitor 26 and resistor 27 are connectedin series across the terminals of winding 23 to form a differentiatingnetwork, the output of which is available at terminal 15 to trigger asucceeding driver stage 60. I

Referring now to the operation of the circuit shown in the drawing, itwill be assumed that initially transistor 10 is not conducting. Thelegend NNC applied to transistor It) stands for normally nonconductive.A negative trigger pulse applied to terminal 15 from source 50 passesvia diode 14 to the base 12 of transistor 10. The transistor istriggered to conduction and thereafter collector and base currents I andl respectively flow in the direction of the arrows as indicated in thedrawing. Collector current I flows through the load 40 and the primaryimpedances of transformers 30 and 20 respectively, and then back toground through the collector supply E Diode 24 is placed across winding21 to prevent the oscillations, or ringing, associated with the recoveryof the transformer at the termination of the current pulse. A diode isnot necessary across winding 31 since oscillations are prevented by theimpedance of resistor 33 reflected into the primary circuit oftransformer 30. Base current I flows through the parallel impedance ofresistor 33 and winding 32 of transformer 30, and then through secondarywinding 22 of transformer 20 to ground as a result of the voltagesinduced by the flow of l hereinafter explained.

The action of transformer 20 on the overall circuit operation will nowbe considered as though transformer 30 were not present. Current Iflowing through winding 21 induces a voltage across winding 22 of such apolarity that the dotted terminal of said latter winding is negativewith respect to the undotted terminal. This negative voltage isimpressed on the base electrode 12 of the transistor and maintains theconduction thereof after the trigger pulse has terminated. The durationof said conduction, or alternately stated, the width of the currentpulse delivered to the load is a function of the magnitude of thecollector current l the characteristics of the magnetic material ofpulse transformer 20, the turns ratio of the windings on transformer 20and the magnitude of the supply voltage E Since the voltage developedacross winding 22 by current I flowing through winding 21 is clamped atthe supply potential E it is assumed that the voltage across winding 22is constant at the E level. The pulse duration At is then givenapproximately by the expression:

where L is the inductance of winding 22 and Ai is the value of collectorcurrent I transformed into the secondary circuit of transformer 20. Theturns ratio of windings 21 and 22 is chosen such that with the minimumvalue of at expected during circuit operation, the pulse transformer 20saturates. When saturation occurs the voltage across winding 22decreases rapidly toward zero, and the transistor deprived of thenegative bias on its base, ceases to conduct. Since the pulse width ofthe load current is dependent on the clamping level, a variable widthconstant current driver can be mechanized simply by clamping the voltageinduced across winding 22 to a variable voltage source instead of to thefixed potential E As hereinbefore mentioned, the amplitude of thecurrent pulse delivered to the load is controlled by transformer 30. Thecombination of resistor 33 and the transformer 30 may be represented byan equivalent primary resistance. Current I flowing through this primaryresistance causes a voltage drop thereacross which is transformed intothe secondary with a value determined by the turns ratio of transformer30. The latter voltage appearing across winding 32 is applied to thebase of transistor 10 and is of such polarity as to tend to decrease theconduction thereof. There is an additional voltage drop appearing acrossthe parallel combination of winding 32 and resistance 33 which resultsfrom the base current I flowing therethrough. In practice, even underworst-case conditions, this voltage is small and has no appreciableeffect on the regulating properties of the instant circuit. Therefore,this latter voltage is neglected in the succeeding consideration ofcircuit op eration.

In the preceding description of the function of transformer 20 it wasnoted that the conduction of the transistor, subsequent to the triggerpulse, was maintained by the voltage generated across winding 22. Itshould now be apparent that the actual bias appearing on the base of thetransistor is the algebraic sum of the voltages appearing respectivelyacross windings 22 and 32. Thus the eifect of transformer 20 on theconduction of the transistor is regenerative, while transformer 30 isdegenerative. Obviously, if the circuit is to supply current pulses to aload, the net effect of the transformers must be regenerative. Since thevoltage across winding 22 is a constant value, as determined by thesupply voltage E the voltage across the secondary of transformer 30 willcontrol the bias on the transistor and thereby the magnitude of thecollector current flowing through the load 40. If the variation in theload impedance results in a tendency for I to increase or decrease froma design value, this tendency is sensed by the transformer 30 and isreflected as a change in the voltage across winding 32. This change insecondary voltage results in a change of the net bias on the transistorof such an instantaneous polarity to cause the collector current 1 toremain at its design value.

It will be assumed that it is desired to have a design value of currentflowing through the load 40[ Since the load current is the collectorcurrent I of the transistor, the bias which must be applied to'thetransistor to obtain the design load current is easily ascertained fromthe transistor characteristic curves which relate collector current tobase-emitter bias. As hereinbefore explained, the voltage appearingacross winding 22 is equal to the supply voltage E Resistor 33 isselected such that the algebraic sum of the voltage appearing across thesecondary circuit of transformer 30 and the supply voltage E is thevalue of bias voltage required to produce the design load current. Ifthe load impedance is diminished, current I will tend to rise above thedesired level. This increase in load current results in a larger voltageacross the equivalent primary resistance of transformer 30 and aproportional increase in the secondary voltage across winding 32 inaccordance with the turns'ratio. This increase in the secondary voltageof transformer 30 causes a less negative bias to appear on thetransistor 10, and the collector current I is adjusted to its designvalue. Conversely, if I tends to decrease from the design value, thevoltage across the secondary circuit of transformer 30 will decrease andthe bias on the transistor will become more negative, thereby increasingthe conduction of the transistor and causing I to return to its designvalue.

An important characteristic of the design of the instant driver circuitis that transistors having different values of ,3 (the ratio ofcollector current to base current) may be substituted for one another inthe circuit without appreciably alfecting its overall operation. Theonly consideration which must be made is that of providing suflicientbase current for a minimum 5: transistor throughout the range ofinstantaneous load currents which may be encountered during circuitoperation.

As mentioned previously, the present driver circuits are amenable totandem operation. The voltage pulse induced across winding 23 oftransformer 20 by load current flowing through winding 21 isdifferentiated by capacitor 26 and resistor 27. The trigger-typevoltages associated respectively with the leading and trailing edge ofthe differentiated pulse appear at terminal 15'. These voltages areapplied to a succeeding driver stage 60 which selects a trigger voltageof the proper polarity to initiate the succeeding current pulse cycle.

From the foregoing description of the invention it is evident that thepresent technique of utilizing the respective regenerative anddegenerative effects of a pair f pulse transformers on a currentamplifying device results in efficient and dependable currentregulation. It must be understood that while a preferred embodiment ofthe invention has been shown, this embodiment is meant to beillustrative only, and is not limitative of the invention. For example,a vacuum tube may be substituted for the transistor; or the pulsetransformers may be replaced with magnetic cores having substantiallyrectangular hysteresis characteristics. Many additional modificationswill be suggested to those skilled in the art, and all such variationsas are in accord with the principles discussed previously are meant tofall within the scope of the appended claims.

What is claimed is:

l. A circuit for delivering a regulated current pulse to a loadcomprising a current amplifying device, the degree of conduction of saiddevice being a function of the voltage applied thereto, first and secondtransformers connected in a series path with said load and said currentamplifying device, said load current flowing in said series path, saidfirst transformer generating a constant voltage in response to the flowof said load current, said constant voltage when applied to saidamplifying device being regenerative with respect to the conductionthereof, said second transformer generating a voltage having a magnitudeproportional to the amplitude of said load current, said latter voltagewhen applied to said amplifying device being degenerative with respectto the conduction thereof, means for applying the voltages generated bysaid first and second transformers concurrently to said amplifyingdevice, said generated voltages producing a resultant voltage forcontrolling the conduction of said device and the correspondingamplitude of load current, said resultant voltage having a polarity tosustain the conduction of said amplifying device throughout the periodof nonsaturation of said first transformer, variations in said loadcurrent during said nonsaturated period resulting in an instantaneouschange in said resultant voltage of such magnitude as to maintain theamplitude of said load current substantially constant, the saturation ofsaid first transformer by said load current resulting in the terminationof said regenerative voltage whereby the resultant voltage applied tosaid amplifying device is of a polarity to terminate the flow of loadcurrent.

2. A circuit for generating pulses of regulated load current comprisinga current amplifying device having at least an input electrode and anoutput electrode, said amplifying device being adapted to supply currentto a load coupled to said output electrode, the amplitude of said loadcurrent being a function of the voltage applied to said input electrodeof said device, first and second transformers, a primary winding and asecondary winding coupled to each of said transformers, said primarywindings being connected in series to said output electrode and saidload, said secondary windings being connected in series to said inputelectrode, impedance means connected in parallel with said secondarywinding of said second transformer, means for applying a trigger pulseto said input electrode for initiating the flow of load current fromsaid amplifying device, said load current flowing through said primarywindings inducing a voltage across each of said secondary windings,means for clamping the voltage induced across the secondary of saidfirst transformer to a fixed potential, said latter induced voltagehaving a polarity which when applied to said input electrode isregenerative with respect to the flow of said load current, thesecondary voltage of said second transformer having a magnitudeproportional to the amplitude of said load current and a polarity whichwhen applied to said input electrode is degenerative with respect to theflow of said load current, said secondary voltages producing a resultantvoltage on said input electrode of said amplifying device, saidresultant voltage determining the degree of conduction of said deviceand the corresponding amplitude of load current, said resultant voltagehaving a polarity to sustain the conduction of said amplifying devicethroughout the period of nonsaturation of said first transformer,variations in said load current during said period resulting in aninstantaneous change in said resultant voltage of such magnitude as tomaintain the amplitude of said load current substantially constant, thesaturation of said first transformer by said load current resulting inthe termination of said regenerative voltage whereby the resultantvoltage applied to said amplifying device is then of such polarity as topreclude the continued conduction of said device and the fiow of loadcurrent.

3. A pulse forming circuit as defined in claim 2 Wherein said clampingmeans comprise a diode having one of its electrodes coupled to a sourceof clamping potential and the other of its electrodes coupled to one endof said secondary winding on said first transformer in such a mannerthat the voltage induced across said latter secondary winding cannotexceed the level of said clamping potential.

4. An electronic circuit for supplying load current pulses havingcontrolled amplitudes and pulse widths comprising a transistor having anemitter, collector and base electrode, said transistor being adapted tosupply current to a load coupled to said collector electrode, theamplitude of said load current being a function of the bias voltageapplied between said emitter and base electrodes, said emitter electrodebeing connected to a reference potential, first and second pulsetransformers, a primary winding and a secondary winding coupled to eachof said transformers, said primary windings being connected in serieswith said collector electrode and said load, said secondary windingsbeing connected in series with said base electrode, impedance meansconnected in pareach of said secondary windings, diode means forclamping the voltage induced across the secondary of said firsttransformer to a fixed potential, said latter induced voltage having apolarity which when applied to said base electrode is regenerative withrespect to the flow of current from said transistor, the secondaryvoltage of said second transformer having a magnitude proportional tothe amplitude of said load current and a polarity which when applied tosaid base electrode is degenerative with respect to the flow of saidload current, said secondary voltages providing a resultant bias voltageon the base of said transistor, said bias determining the degree ofconduction of said transistor and the corresponding amplitude of loadcurrent, the polarity of said bias voltage being suitable for sustainingthe conduction of said transistor throughout the period of nonsaturationof said first transformer, variations in said load current during saidnonsaturated period resulting in an instantaneous change in said biasvoltage of such magnitude as to maintain the amplitude of said loadcurrent substantially constant, the saturation of said first transformerby said load current resulting in the termination of said regenerativevoltage, whereby the bias applied to said transistor is then of suchpolarity as to preclude the continued conduction thereof.

5. A driver circuit for supplying a sequence of regulated current pulsesto a load comprising a PNP junctiontype transistor having an emitter,collector and base electrode, said transistor being adapted to supplycurrent to a load connected to said collector electrode, the amplitudeof said load current being a function of the bias voltage appliedbetween said emitter and base electrodes, said emitter electrode beingconnected to ground potential, first and second pulse transformers, aprimary winding and first and second secondary windings coupled to saidfirst transformer, a primary winding and a secondary winding coupled tosaid second transformer, said primary windings being connected in serieswith said collector electrode and said load, said first secondarywinding of said first transformer and the secondary winding of saidsecond transformer being connected in series'with said base electrode, aresistive element connected in parallel with said first secondarywinding of said first transformer, means coupled to said base electrodefor applying a short duration negative trigger pulse thereto forinitiating the conduction of said transistor, the flow of said loadcurrent through said primary windings inducing a voltage across each ofsaid secondary windings, diode means for clamping the voltage inducedacross said first secondary winding of said first transformer to a fixedpotential, said latter induced voltage having a negative polarity whichwhen applied to the base electrode of said transistor is regenerativewith respect to the flow of load current, the secondary voltage of saidsecond transformer having a magnitude proportional to the amplitude ofsaid load current and a positive polarity which when applied to the baseelectrode of said transistor is degenerative with respect to the flow ofsaid load current, the algebraic sum of said regenerative anddegenerative voltages appearing as a bias voltage on the base of saidtransistor, said bias determining the degree of conduction of saidtransistor and the corresponding amplitude of load current, the negative polarity of said bias voltage tending to sustain the conduction ofsaid transistor throughout the period of nonsaturation of said firsttransformer, variations in said load current during said nonsaturatedperiod resulting in an instantaneous change in said bias voltage ofsuchmagnitude as to maintain the amplitude of said load currentsubstantially constant, the saturation of said first transformer by saidload current resulting in the termination of said regenerative voltage,whereby said bias is then of positive polarity which precludes thefurther conduction of said transistor, means for difierentiating thevoltage pulse induced across said second secondary winding of said firsttransformer, the differentiated output pulse'which occurs in phase withthe cessation of conduction of said transistor being suitable fortriggering a succeeding driver circuit.

References Cited in the file of this patent UNITED STATES PATENTSBennett Mar. 6, 1951 Hepp Jan. 15, 1952 Light Sept. 30, 1958 Rogers May12, 1959 Finkelstein et -al Feb. 23, 1960 FOREIGN PATENTS Great BritainDec. 2, 1953

1. A CIRCUIT FOR DELIVERING A REGULATED CURRENT PULSE TO A LOADCOMPRISING A CURRENT AMPLIFYING DEVICE, THE DEGREE OF CONDUCTION OF SAIDDEVICE BEING A FUNCTION OF THE VOLTAGE APPLIED THERETO, FIRST AND SECONDTRANSFORMERS CONNECTED IN A SERIES PATH WITH SAID LOAD AND SAID CURRENTAMPLIFYING DEVICE, SAID LOAD CURRENT FLOWING IN SAID SERIES PATH, SAIDFIRST TRANSFORMER GENERATING A CONSTANT VOLTAGE IN RESPONSE TO THE FLOWOF SAID LOAD CURRENT, SAID CONSTANT VOLTAGE WHEN APPLIED TO SAIDAMPLIFYING DEVICE BEING REGENERATIVE WITH RESPECT TO THE CONDUCTIONTHEREOF, SAID SECOND TRANSFORMER GENERATING A VOLTAGE HAVING A MAGNITUDEPROPORTIONAL TO THE AMPLITUDE OF SAID LOAD CURRENT, SAID LATTER VOLTAGEWHEN APPLIED TO SAID AMPLIFYING DEVICE BEING DEGENERATIVE WITH RESPECTTO THE CONDUCTION THEREOF, MEANS FOR APPLYING THE VOLTAGES GENERATED BYSAID FIRST AND SECOND TRANSFORMERS CONCURRENTLY TO SAID AMPLIFYINGDEVICE, SAID GENERATED VOLTAGES PRODUCING A RESULTANT VOLTAGE FORCONTROLLING THE CONDUCTION OF SAID DEVICE AND THE CORRESPONDINGAMPLITUDE OF LOAD CURRENT, SAID RESULTANT VOLTAGE HAVING A POLARITY TOSUSTAIN THE CONDUCTION OF SAID AMPLIFYING DEVICE THROUGHOUT THE PERIODOF NONSATURATION OF SAID FIRST TRANSFORMER, VARIATIONS IN SAID LOADCURRENT DURING SAID NONSATURATED PERIOD RESULTING IN AN INSTANTANEOUSCHANGE IN SAID RESULTANT VOLTAGE OF SUCH MAGNITUDE AS TO MAINTAIN THEAMPLITUDE OF SAID LOAD CURRENT SUBSTANTIALLY CONSTANT, THE SATURATION OFSAID FIRST TRANSFORMER BY SAID LOAD CURRENT RESULTING IN THE TERMINATIONOF SAID REGENERATIVE VOLTAGE WHEREBY THE RESULTANT VOLTAGE APPLIED TOSAID AMPLIFYING DEVICE IS OF A POLARITY TO TERMINATE THE FLOW OF LOADCURRENT.